1. Technical Field
The present invention relates to wireless communication and, more particularly, to an apparatus and method for uplink transmission in a wireless communication system.
2. Related Art
A 3GPP (3rd Generation Partnership Project) based on a WCDMA (Wideband Code Division Multiple Access) radio access technique is being extensively developed all over the world. An HSDPA (High Speed Downlink Packet Access), which may be defined as a first evolution of the WCDMA, provides a radio access technique with a highly competitive edge in the mid-term future to the 3GPP. However, as requirements and expectations of users and service providers are continuously increasing and development of competing wireless access techniques is ongoing, a new technical evolution from the 3GPP is requested to ensure competitiveness in the future. The requirements include a reduction in costs per bit, an increase in service availability, the flexible use of frequency bands, a simple structure and an open interface, proper power consumption of terminals (i.e., user equipments (UEs)), and the like.
One of systems considered in the next generation is an OFDM (Orthogonal Frequency Division Multiplexing) system that can attenuate an inter-symbol interference effect with a low complexity. In the OFDM, serially inputted data symbols are converted into N number of parallel data symbols, which are then included in N number of separated subcarriers, so as to be transmitted. The subcarriers maintain orthogonality in a frequency domain. The respective orthogonal channels experience mutually independent frequency selective fading, and the intervals of transmitted symbols are lengthened to minimize the inter-symbol interference.
In the OFDM-based wireless communication system, it is important to match time synchronization between a UE and a base station (BS) to minimize interference among users. A random access procedure is performed for uplink synchronization between the UE and the BS. During the random access procedure, the UE matches time synchronization based on a time alignment value transmitted from the BS. When the uplink synchronization is made, the UE runs a time alignment timer. While the time alignment timer is running, the UE and the BS are considered to be in the uplink synchronization. If the time alignment timer expires or does not run, the UE and the BS are not in synchronization, so uplink transmission, except for a random access preamble transmission, is not made.
In general, when the uplink synchronization has not been made because the time alignment timer expires or does not run, the UE releases control resource and obtains time synchronization, and then reconfigures control resource for uplink transmission.
In this case, however, if the uplink synchronization has not been made, uplink data could be transmitted only if the uplink synchronization is made. That is, releasing the control resource and reconfiguring it again is ineffective and causes a time delay.
Thus, a method for effective uplink transmission even when the time alignment timer expires or does not run is required.